Survivors, rescuers and victims' relatives have gathered at Ground Zero in New York to commemorate the opening of the 9/11 Memorial Museum.

President Barack Obama took part in the dedication ceremony, calling the museum "a sacred place of healing and of hope".

He said: "Here at this memorial, this museum, we come together to stand in the footprints of two mighty towers graced by the touch of eternal waters.

"We look into the face of nearly 3,000 souls. We can touch their names and hear their voices.

"Here, we tell their story so that generations yet to be born never forget."

Image Caption:Mr Obama toured the museum with former New York Mayor Michael Bloomberg

The president recounted how one man, 24-year-old Welles Crowther, sacrificed his life so that others could escape the burning World Trade Center.

He said: "In those awful moments after the South Tower was hit some of the injured huddled in the wreckage of the 78th floor.

"The fire was spreading, the air was filled with smoke, it was dark and they could barely see, and it seemed as if there was no way out.

"Then came a voice, clear and calm, saying he had found the stairs."

It was Mr Crowther, known only to those he helped save by the red bandana he wore that day.

One of Mr Crowther's red bandanas is among the more than 10,000 artefacts on display at the museum.

Video:Obama Dedication At 9/11 Museum

His mother, Alison, told the audience on Thursday that she hoped it would remind visitors "how people helped each other that day, and that they will be inspired to do the same in ways both big and small".

She said: "This is the true legacy of September 11."

The museum, which cost $700m (£417m) to complete, is located 70ft underground and traces the original foundations of the fallen twin tours.

The 110,000 sq ft exhibition includes 23,000 still images, 500 hours of video and film and nearly 2,000 oral histories on the events of that day.

Video:9/11 Museum Opens At Ground Zero

The museum also commemorates the September 11 attack on the Pentagon and hijacked United Airlines Flight 93, which crashed near Shanksville, Pennsylvania.

There are also exhibits pertaining to the 1993 World Trade Center bombing.

Prior to Thursday's dedication ceremony, Mr Obama toured the expansive hall with former New York Mayor Michael Bloomberg.

First lady Michelle Obama, former President Bill Clinton and former Secretary of State Hillary Clinton also toured the museum.

Video:Transfer Of 9/11 Remains

Former New York Mayor Rudy Giuliani was also on-hand, along with current Mayor Bill de Blasio, New York Governor Andrew Cuomo and New Jersey Governor Chris Christie.

The museum opens to the general public on May 21. Officials hope the $24 entrance fee will generate $40m per year to help offset an annual operating budget of $60m.